Tungsten-hafnium-oxygen alloys



United States Patent 3,434,811 TUNGSTEN-HAFNIUM-OXYGEN ALLOYS StephenFoldes, Cleveland, Ohio, assignor to General Electric Company, acorporation of New York No Drawing. Filed Feb. 26, 1965, Ser. No.435,725 Int. Cl. B22f 3/10; C22c 27/00 US. Cl. 29-1825 5 Claims ABSTRACTOF THE DISCLOSURE The present invention relates generally totungsten-base alloys useful in high temperature applications, and morespecifically relates to such alloys containing both hafnium and oxygenin material amounts.

Previously known alloys of tungsten containing hafnium generally alsoinclude carbon in combination with the hafnium constituent. All alloysare subject to limitations on their utility due to their mechanical andmetallurgical characteristics. In particular, the utilities of knowntungsten-hafnium-carbon alloys have limits de pending upon thefabricability of the metal, especially in the alloys containing largeramounts of hafnium and carbon, and also depending on such other factorsas stability of hafnium carbides in the tungsten matrix. Each of thesefactors can be affected strongly by the contained amounts andproportions of alloying additives including and in addition to hafniumand carbon.

Although in certain cases one alloy system cannot be categoricallystated to be superior to another, it often can be determined thatcertain properties of one type of alloy are significantly more useful incertain applications than are related properties of another type ofalloy. Thus, it is desirable to provide different types of alloy systemsthat may be found to be superior in certain applications to known alloysystems.

Accordingly, it is an object of the present invention to providetungsten-base alloys containing dispersoids, which alloys are differentfrom and in some aspects superior to many known tungsten-base alloys incertain characteristics.

It is further the object of the invention to provide such alloys thatare superior to many known tungsten-base alloys in workability andfabricability.

Still another object of the invention is to provide such alloys whichare superior to many known tungsten-base alloys in applications atelevated temperatures.

Briefly stated, the present invention in one form providestungsten-hafnium-oxygen alloys having desirable characteristicsdifferent from, and in some cases superior to presently known alloys.Alloys of the invention contain, by weight, about: 1-7% hafnium,0.030.l2% oxygen, not more than of metal selected from the groupconsisting of columbium, molybdenum, tantalum, rhenium and mixturesthereof, not more than 2% of metal selected from the group consisting ofzirconium, titanium and vanadium and mixtures thereof, and not more than0.25% boron, the balance essentially all tungsten. Preferably, theoxygen content of the alloys of the invention is 0.06-0.09%. Theelements specified in amount not more than certain percentages areentirely optional, and the term not more than is meant to include anamount of zero. Specifically preferred alloys of the invenice tioninclude the preferred range of oxygen content along with hafnium inamounts of about 1%, 2.9 or 3%, and 6.6 or 7%. Percentages herein aregiven by weight except where specified otherwise.

By the use of large amounts of oxygen which, even in smallest amounts,was considered by the prior art to be deleterious and to render alloysunusable, the alloys of the present invention are provided withstrengths and stabilities that are quite useful and in some casessuperior to those previously generally known in tungsten-base alloys.While previously known alloys were considered to require that oxygencontents be no more than 50 or even 35 parts per million by weight(p.p.m.), I have foun that the alloys of the invention beneficiallycontain oxygen within the limits of 300-1200 p.p.m., and preferably600900 p.p.m. oxygen.

Alloys of the invention have been prepared by mixing together freshlyreduced tungsten metal powders and hafnium hydride powders according topredetermined nominal compositions, pressing them into compacts andsintering in vacuum. An analysis of the starting materials is presentedin Table I below with the quantities given in p.p.m. except whereexpressed otherwise.

TABLE I.ANALYTIOAL DATA AND PARTICLE SIZE OF STARTING MATERIAL Inaddition to the impurities noted in the table, the tungsten containedless than 10 ppm. of other impurities. These materials were premixed ina twin shell blender, and then thoroughly blended for about four hoursin a tungsten rod mill. Compacts were then made by hydrostatic pressingin a rubber sleeve at a pressure of about 35,000 p.s.i.

Following a vacuum pre-sintering treatment at 1050 C. for two hours, theingots were finally sintered at 2800 C. for two hours in a dynamicvacuum of less than 10- torr. Above the dissociation temperature ofhafnium hydride of about 600 C., the small amounts of tungsten oxide onthe surface of the tungsten metal powder continued to evaporate andreact with the nascent hafnium surfaces, thus resulting in a significantpickup of oxygen by hafnium during sintering. Since material quantitiesof carbon were not present in the compacts, the oxygen became usefullyassociated with the hafnium rather than being volatilized out of thecompact. The hafnium oxide dispersoid particles thus formed perform auseful function in greatly strengthening the alloys while also allowingthem to be worked at elevated temperatures. Subsequent to the sinteringoperation, the alloys were analyzed, and the results of these tests arepresented in Table II below. The values are in p.p.-m. except forhafnium which is expressed in percentages.

TABLE IL-ALLOY COMPOSITIONS AND ANALYSES Analysis O N H The sinteredingots were from 92-95% of theoretical density. They were machined tocylinders one inch in diameter by 2.5 inches long with a 45 chamferednose. The cylinders were extruded at a 10:1 ratio to 0.350 inch diameterrods in a high energy rate extrusion apparatus. Hardness and grain sizemeasurements were taken on the as-extruded alloys and are presented inTable III below. VPH stands for Vickers pyramid hardness.

TABLE III.HARDNESS AND GRAIN SIZE Extrusion Grain Size, VPH, Temp., 0.microns kgt/mmfi Nominal Composition:

W-lHi 2, 050 27 378 W3Ht 2, 100 7 477 W-7Ht 2, 310 9 517 TABLE IV.HIGHTEMPERATURE TENSILE DATA Temper- UTS, 0.2% YS, Elongation, ague, K s.i.K s.i. percent Nominal Composition:

1, 649 15. 4 8. 3 65. 1 W 1, 927 8. 9 4. 9 36. 8 2, 206 6. 3. 4 32. 4 1,649 48. 2 30. 4 38. 2 W-lHf 1, 927 26. 9 18. 1 38. 6 2, 206 12. 6 11. 112.7 1, 649 63. 7 47. 20. 5 W-3Hf 1, 927 41. 4 36. 1 19. 9 2, 206 21. 018. 5 13. 8 1, 649 W-7Hf 1, 927 49. 1 30. 1 19. 5

It can be seen from the table that these alloys are significantlystronger than unalloyed tungsten at elevated temperatures. In addition,the alloy containing 7% hafnium is considerably stronger than mostpreviously known tungsten-base alloys.

It is contemplated by the appended claims to cover any suchmodifications as fall within the true spirit of the scope of thisinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A sintered tungsten-base alloy consisting essentially of about, byweight: 17% hafnium, 0.03-0.12% oxygen, not more than 10% of metalselected from the group consisting of columbium, molybdenum, tantalum,rhenium and mixtures thereof, not more than 2% of metal selected fromthe group consisting of zirconium, titanium and vanadium and mixturesthereof, and not more than 0.25% of boron, the balance essentially alltungsten, said alloy containing hafnium oxide dispersoid particlesthere- 2. A sintered tungsten-base alloy consisting essentially ofabout, by weight: 17% hafnium, 0.06-0.09% oxygen, not more than 10% ofmetal selected from the group consisting of columbium, molybdenum,tantalum, rhenium and mixtures thereof, not more than 2% of metalselected from the group consisting of zirconium, titanium, and vanadiumand mixtures thereof, and not more than 0.25% of boron, the balanceessentially all tungsten, said alloy containing hafnium oxide dispersoidparticles there- 3. A sintered tungsten-base alloy consistingessentially of about, by weight: 1% hafnium, 0.06-0.09% oxygen, thebalance essentially all tungsten, said alloy containing hafnium oxidedispersoid particles therein.

4. A sintered tungsten-base alloy consisting essentially of about, byweight: 2.9% hafnium and 0.060.09% oxygen, the balance essentially alltungsten, said alloy containing hafnium oxide dispersoid particlestherein.

5. A sintered tungsten-base alloy consisting essentially of about, byweight: 6.6% hafnium and 0.060.09% oxygen, the balance essentially alltungsten, said alloy containing hafnium oxide dispersoid particlestherein.

References Cited UNITED STATES PATENTS 3,116,145 12/1963 Semchyshen -1763,150,971 9/1964 Weisert et al. 75176 3,177,076 4/1965 Timmons et al.75176 3,181,946 5/1965 McAndreW et al. 75174 3,243,291 3/1966 Dickinson75-176 OTHER REFERENCES Nb, Ta, Mo and W Quarrell, Elsevier PublishingCompany, N.Y., 1961, relied on pages 321 and 332.

Tungsten Alloys of High Melting Point, Kieffer et al., Journal of theLess Common Metals, vol. 1, 1959, relied on pages 19-33.

CHARLES N. LOVELL, Primary Examiner.

U.S. Cl. X.R. 75176

